In addition, proponents and land managers should refer to the Recovery Plan (where available) or the Conservation Advice (where available) for recovery, mitigation and conservation information.
|EPBC Act Listing Status||Listed marine|
|Adopted/Made Recovery Plans|
|Policy Statements and Guidelines||
Marine bioregional plan for the Temperate East Marine Region (Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), 2012aa) [Admin Guideline].
Marine bioregional plan for the North Marine Region (Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), 2012x) [Admin Guideline].
Marine bioregional plan for the North-west Marine Region (Department of Sustainability, Environment, Water, Population and Communities (DSEWPaC), 2012y) [Admin Guideline].
Sea snakes - A Vulnerability Assessment for the Great Barrier Reef (Great Barrier Reef Marine Park Authority (GBRMPA), 2011f) [Admin Guideline].
Federal Register of
Declaration under section 248 of the Environment Protection and Biodiversity Conservation Act 1999 - List of Marine Species (Commonwealth of Australia, 2000c) [Legislative Instrument].
|Scientific name||Aipysurus duboisii |
This is an indicative distribution map of the present distribution of the species based on best available knowledge. See map caveat for more information.
The current conservation status of the Dubois' Seasnake, Aipysurus duboisii, under Australian Government legislation, is as follows:
National: Listed as a marine species under the Environment Protection and Biodiversity Protection Act 1999.
Scientific name: Aipysurus duboisii
Common name: Dubois' Seasnake
The Dubois' Seasnake is moderately built snake of variable colour. Darker specimens are usually found west of Torres Strait, and paler specimens to the east. Typically, the concealed surface of the scale contrasts with the dark brown exposed surface. This produces a reticulate (net-like) pattern in the body scales when the body is extended. The scales of the lower flanks are more typically white, forming wedge-shaped pale areas extending to the upper surface. All head shields with the exception of the rostral scale and the nasals are fragmented into small irregular scales. The body scales are imbricate and in 19 rows at the mid-body. Ventral scales are broad and vary from 150–165. The anal scale is divided. Subcaudal scales vary from 23–35. The Dubois' Seasnake grows to 109 cm in snout vent length (Cogger 1975, 1996; Fry et al. 2001; Smith 1926).
The Dubois' Seasnake occurs between Exmouth Gulf in Western Australia (Storr et al. 1986) and Hervey Bay in Queensland (Limpus 1975); and on Ashmore Reef and the Sahul Shelf (Minton & Heatwole 1975).
The Dubois' Seasnake is found in tropical northern Australia (Cogger 1996), Papua New Guinea (De Rooij 1917) and New Caledonia (Laboute & Magnier 1979).
The species occurs in the Great Barrier Reef Marine Park, and at Ashmore Reef in Western Australia which is a Commonwealth Reserve (Guinea & Whiting 2005).
The Dubois' Seasnake is most often observed in shallow water near protected coral reefs at depths of 3–4 m (McCosker 1975), but it has also been caught in trawling nets at depths of approximately 45 m (Dunson 1975b). During trawling on the northern Australian continental shelf, the species was most frequently caught at depths of 20–50 m (Ward 2000).
Sea snakes are air breathing reptiles and must come to the surface to breathe, however they can spend from 30 minutes to two hours diving between breaths. They have one elongate cylindrical lung that extends for almost the entire length of their body which is very efficient for gas exchange. They also carry out cutaneous respiration whereby oxygen diffuses from sea water across the snake's skin into the blood. The waste product, carbon dioxide, is then diffused out of the snake's body, via the skin (Heatwole 1999).
Sea snakes have nostril valves that prevent air entering the lung while underwater. Nostril valves open inwards and are held shut from behind by erectile tissue engorged with blood (Heatwole 1999).
Sea snakes are able to avoid excess salt accumulation from sea water using a salt excreting gland, known as the posterior sublingual gland, which sits under the tongue. Sea snakes shed their skin every two to six weeks, which is more frequently than land snakes and more often than needed for growth alone. The process involves rubbing the lips against coral or other hard substrate to loosen the skin. The snake's skin is then anchored to the substrate as it crawls forward, leaving the skin turned inside out behind it. Skin shedding allows sea snakes to rid themselves of fouling marine organisms such as algae, barnacles and bryozoans (Heatwole 1999).
The Dubois' Seasnake, like most sea snakes, is viviparous, that is giving birth to live young (Cogger 2000). In addition, male sea snakes have two penises called hemipenes, and each is an autonomous independently functioning penis, though only one is used during mating. Mating takes place for long periods and sea snakes must surface for air during that time. The female controls her breathing and, as she swims to the surface, the male is pulled along via the hemipenis. Males are unable to disengage until mating is finished (Cogger 2000; Heatwole 1999).
More specifically, Dubois' Seasnakes has been found to give birth to a mean of 4.5 young (with a maximum of six and a standard error of 1.0, in a sample of four females) (Fry et al. 2001). The large size of young and the numbers per brood resulted in this species having the highest relative clutch mass of the sea snake species caught during trawling in northern Australia. In northern Australia, gestation lasts six to seven months, and births occur between March and June. Females appear to reproduce every year (Fry et al. 2001).
The Dubois' Seasnake eats reef fishes, including eels, Gymnothorax undulatus (Muraenidae), blennies Salarias fasciatus (Blennidae), parrotfish Scarus sp. (Scaridae), surgeonfish Acanthuses xanthopterus (Acanthuridae) and the scorpaenid Richardsonichthys leucogaster (McCosker 1975).
The Dubois' Seasnake is thought to feed in the early evening (McCosker 1975).
The Dubois' Seasnake is sometimes washed ashore in Hervey Bay, most likely a result of ocean currents carrying it south from northern Queensland (Limpus 1975).
Sea snakes that inhabit coral reefs and lagoons can be surveyed by travelling slowly (at about four knots) along transects in a small boat and visually identifying snakes observed within 3 m of the path of the boat. Species can be distinguished by this method if the water is up to 3 m deep. At low tide, surveys can be done on foot, for example by searching the reef flat along transects that are 1000 m long and 20 m wide (Guinea & Whiting 2005).
For close up identification, sea snakes that are swimming on the surface of the water can be captured using a dip net employed from a small boat (Limpus 1975). Snakes that are underwater and either active or resting can also be hand-netted by an individual snorkelling or scuba diving, using a cylindrical net 300 mm in diameter and 1700 mm long, with 10 mm mesh. With the aid of protective gloves the snake is gently grasped through the mesh at the base of the net, drawing the snake in until the top of the net can be twisted shut (Guinea & Whiting 2005; Guinea in press). Alternatively, snakes that are resting can be captured by grasping them behind the head and by the mid-body simultaneously. Pillstrom tongs and gloves can be used, although mechanical restraint may injure the snake and increase its aggressiveness (Heatwole 1975).
Prawn trawling has been identified as a major threat to sea snakes due to: their life history (low fecundity and longevity); and demographic factors whereby much of the species' distribution coincides with those areas and depths where prawn trawling occurs (Marsh et al. 1993; Milton et al. 2009). Sea snakes are caught in the bycatch of trawls, and it is estimated that approximately 50% of individuals caught in trawls die by drowning or being crushed by the weight of the catch (Milton et al. 2009; Wassenberg et al. 2001). While sea snakes can naturally remain submerged for up to two hours, the conditions within the net will affect the sea snakes (Wassenberg et al. 2001). These conditions include the physical weight of the catch, the composition of the catch (including poisonous, spiny or abrasive animals) and the interaction of the catch with the seafloor. Survival has been found to depend on a few factors including when the sea snake enters the net (early or late in the tow), the duration of the trawl, the weight of the catch, how the sea snake is treated on the deck and the sea snake's morphology (Wassenberg et al. 2001).
The Dubois' Seasnake is caught during trawling operations. The species represented 0.9% of the bycatch caught during prawn trawling on the northern Australian continental shelf (Ward 1996b), and 4% of the bycatch caught during fish trawling (Ward 1996a). In studies carried out during the 1970s, Dubois' Seasnakes represented 7% of the snakes caught during trawling in the Timor Sea, and 0.5% to 2% of those caught during research and prawn trawling in the Gulf of Carpentaria and north east Queensland (Redfield et al. 1978; Shuntov 1971; Wassenberg et al. 1994).
Bycatch Reduction Overview
In the early 2000s, the mandatory use of Turtle Excluder Devices (TEDs) was introduced to all Australian trawl fisheries to reduce turtle bycatch. In addition, the Bycatch Reduction Devices (BRDs) were introduced to most Australian prawn trawl fisheries to reduce the bycatch of non-targeted species including sea snakes. BRDs are escape grids or openings designed to enable non-target marine animals to swim out of the net, while TEDs are hard grids placed in trawl nets to exclude turtles and other large animals. An illustration of these devices can be found here: TED/BRD. Both TEDs and BRDs assist in the conservation of sea snakes by: reducing the number of fish caught which decreases the weight of the catch, thus, reducing the physical damage to sea snakes caught in the nets; and, enabling sea snakes caught to escape (Wassenberg et al. 2001). As a result of the mandatory introduction of these devices, Australia’s state and commonwealth prawn trawl fisheries must now have both a TED and a second BRD installed in every trawl net (Courtney et al. 2010).
A range of studies have been conducted to evaluate the effectiveness of BRDs, as well as TEDs and BRDs used simultaneously, on sea snakes. For example, Wassenberg et al. (2001) suggested that the mortality rates should decline with the introduction of BRDs due to the reduced weight of the bycatch in nets as well as increased escapement by snakes. Brewer et al. (2006) concluded that the simultaneous use of TEDs and BRDs used by fishers in the Northern Prawn Fishery (NPF) had little effect (i.e. 5%) on excluding snakes from trawl nets. However, they found that the performance of BRDs alone could be improved if placed closer to the codend (the trailing end of the net where fish are finally caught). More recently, through improvement in design, the Fisheye BRD was similarly identified as capable of reducing sea snake bycatch and its effectiveness dependant on distance from the codend (Courtney et al. 2010). Testing of the Yarrow Fisheye BRD (Heales et al. 2008) and the Popeye Fishbox BRD (Raudzens 2007) in the NPF demonstrated their high potential for reducing sea snake catch rates with no adverse reduction in targeted prawn catch rates.
Prawn Trawling Crew Member Programs
Prawn trawling has been found to have a negative impact on protected sea snake populations (Milton et al. 2008). In 2003, a Crew Member Observer (CMO) program was established in the Northern Prawn Fishery (NPF). The program aimed to collect data on bycatch such as composition, catch rates and distribution during both NPF tiger and banana prawn fishing seasons. The initiative required the Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Australian Fisheries Management Authority (AFMA) to jointly run annual industry workshops to train the crew in the identification, photographing and recording of sea snakes from bycatch. During the 2003–2005 seasons, 21 crew member observers on 17 vessels collected data from 7602 prawn trawls. The observers recorded 4131 sea snakes from 12 species, with over half being photographed for identification and length estimation (Milton et al. 2008).
This CMO program has been used in conjunction with logbooks, requested industry collections, scientific observers and fishery-independent surveys for long term bycatch monitoring solutions, and reflects the NPF's commitment to the sustainability of all species impacted by its fishing activities (Milton et al. 2008). From 2005 to 2007, Dubois' Seasnake was found to be one of the most common species encountered (Milton et al. 2008).
Another research project (which ran between July 2005 and October 2007), established the Crew Member Program (CMP) to provide detailed information on the catch composition and catch rates of sea snake species and estimates of the within-trawl mortality rate of snakes in the Queensland otter and beam trawl fishery (Courtney et al. 2010). Sixty-seven crews collected data from all of the major east coast trawl fishing sectors. Additional data were obtained from research charters, research surveys and the fishery observer program. Detailed information was collected from a total of 8289 trawls that reported catching 3910 sea snakes. The study found that the highest catch of sea snakes was in redspot king prawn fishery due to an overlap with sea snake habitat.
Current Bycatch Reduction Methods and Effectiveness
Results from the CMP indicate that sea snake bycatch in the Queensland trawl fishery can be significantly reduced by using properly designed and installed BRDs, with no significant reduction in targeted prawn catch rates. Of the BRDs tested (the standard codend with no BRD, Fisheye BRD, square mesh codend BRD and square mesh panel BRD), the CMP found that the Fisheye BRD was the most effective device at excluding snakes i.e. 63% reduction compared to the standard net, with no significant effect on the catch rate of marketable (≥ 20 mm carapace length) prawns. The Fisheye BRD was also the most effective device for excluding bycatch of non-targeted species with a 33% reduction in bycatch rate compared to the standard net (Courtney et al. 2010). Furthermore, the square mesh codend was found to also be highly effective at excluding both sea snakes and other bycatch, with reductions of 60% and 31% respectively, compared to the standard net. However, the effectiveness of square mesh codend was considered to be limited by the maximum size of the square meshes which would provide too small an exit for large snakes (Courtney et al. 2010). Milton and colleagues (2009) found that the commonly used Fisheye BRD also had good exclusion (43% reduction in bycatch by weight) when placed at a distance of 66 meshes from the codend. Where sea snake mortality is high (eg area or sector related), more recent studies have suggested that the device should be placed closer to the codend, that is, 50 meshes (Courtney et al. 2010).
As part of the CMO program, tests undertaken on the Popeye Fishbox BRD, conducted by AFMA in the NPF in the Gulf of Carpentaria, reported an 87% reduction in the catch rate of sea snakes when the device was installed 70 meshes from the codend, with no significant effect on prawn catch rates (Raudzens 2007). However, repositioning the device to 100 meshes from the codend lowered the exclusion rate of bycatch of non-targeted species, thus making it less effective for sea snakes. Brewer and colleagues (2006) similarly found that there was no decrease in sea snake bycatch in the NPF when the BRD was placed at a distance of 120 meshes from the codend (i.e. maximum allowable distance under Australian law).
As shown from the above findings, the distance of the BRD from the codend significantly affects its ability to exclude bycatch of non-targeted species including sea snakes. Even if the most effective BRD is implemented, its performance will be greatly compromised unless an appropriate maximum distance from the drawstring of the codend is also specified (Courtney et al. 2010).
Additional factors that will reduce bycatch of sea snakes include the detection of reduced water flow and the length of hauls (Milton et al. 2009; Wassenberg et al. 2001). For a BRD to be effective, it must also enable the sea snakes to detect the reduced flow posterior to the device (Milton et al. 2009). When tested, the Fishbox BRD was found to have a relatively large region of reduced flow posterior to the device (Heales et al. 2008). The length of hauls has been found to also impact bycatch rates, with shorter hauls reducing the volume of bycatch which in turn increase the survival chances of sea snakes (Milton et al. 2009; Wassenberg et al. 2001).
Marine bioregional plans have been developed for four of Australia's marine regions - South-west, North-west, North and Temperate East. Marine Bioregional Plans will help improve the way decisions are made under the EPBC Act, particularly in relation to the protection of marine biodiversity and the sustainable use of our oceans and their resources by our marine-based industries. Marine Bioregional Plans improve our understanding of Australia's oceans by presenting a consolidated picture of the biophysical characteristics and diversity of marine life. They describe the marine environment and conservation values of each marine region, set out broad biodiversity objectives, identify regional priorities and outline strategies and actions to address these priorities. Click here for more information about marine bioregional plans.
Dubois' Seasnake has been identified as a conservation value in the North-west (DSEWPaC 2012y), North (DSEWPaC 2012x) and Temperate East (DSEWPaC 2012aa) marine regions. The "species group report card - marine reptiles" for the North-west (DSEWPaC 2012y), North (DSEWPaC 2012x) and Temperate East (DSEWPaC 2012aa) marine regions provide additional information.
No threats data available.
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Cogger, H.G. (2000). Reptiles and Amphibians of Australia - 6th edition. Sydney, NSW: Reed New Holland.
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This database is designed to provide statutory, biological and ecological information on species and ecological communities, migratory species, marine species, and species and species products subject to international trade and commercial use protected under the Environment Protection and Biodiversity Conservation Act 1999 (the EPBC Act). It has been compiled from a range of sources including listing advice, recovery plans, published literature and individual experts. While reasonable efforts have been made to ensure the accuracy of the information, no guarantee is given, nor responsibility taken, by the Commonwealth for its accuracy, currency or completeness. The Commonwealth does not accept any responsibility for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the information contained in this database. The information contained in this database does not necessarily represent the views of the Commonwealth. This database is not intended to be a complete source of information on the matters it deals with. Individuals and organisations should consider all the available information, including that available from other sources, in deciding whether there is a need to make a referral or apply for a permit or exemption under the EPBC Act.
Citation: Department of the Environment (2013). Aipysurus duboisii in Species Profile and Threats Database, Department of the Environment, Canberra. Available from: http://www.environment.gov.au/sprat. Accessed Thu, 5 Dec 2013 22:13:53 +1100.